In portable consumer electronics personal listening audio devices, such as cellular phones, smart phones, and loose fitting headsets known as ear buds that may be connected to tablet computers and laptop computers, the listening device often does not have sufficient passive noise attenuation. For instance, the more comfortable, loose fitting ear bud is often preferred, which provides lesser passive ambient noise reduction than a larger and heavier yet better sealing outside-the-ear unit, or a completely sealed inside-the-ear-canal earphone. In addition, a user is often moving around with such a listening device, e.g. while walking or jogging. In the case of a smart phone that is being used in handset mode (against the ear), the phone is held against the user's ear differently by different users, and also tends to move around during a phone call. These user-specific factors change the acoustic environment or acoustic loading of the listening device in real-time. As a result, the use of an adaptive ANC system has been suggested, to help improve the user's listening experience by attempting to produce a quieter environment.
The ANC system produces an “anti-noise” sound wave through an earpiece speaker (e.g., the “receiver” in a smartphone handset, or the speaker driver within an earphone housing) in such a way, that is, having a certain spectral content, that is intended to destructively interfere with or cancel the ambient or background noise sound that would otherwise be heard by the user. Attempts have also been made to improve the performance of the ANC system in personal listening devices, by making the system adaptive. An adaptive filter and an adaptive controller are provided, which aim to model the different parts of the acoustic environment that is surrounding the user, or the various acoustic paths leading to the user's eardrum. Based on sensing the acoustic background noise using a reference microphone, and the residual “cancelled” noise using an error microphone, a feedforward ANC system adapts or continuously changes the state of its adaptive filter in real-time so as to produce an anti-noise signal that better cancels the offending or unwanted noise.